90 model dead tach.

[obsidian]

I've searched multiple times and have read about the little noise filter. However I read that someone just jumped the wires and the tach worked.

So, is the noise filter required?

I also read that there was an attachment/sensor on the stock 90 TB that is required to make the tach work. Is there truth to this?

Most of the threads I found were dead and hadn't been updated with a fix so I'm asking here.

Thanks for looking.

------------------------------UPDATE [FIX]------------------------------

So today Sep 19th, 2011, I have found what I've needed to know for many many days. And this is VERY good news for the 90 guys.

This fix is so simple that it's mind boggling.

Ways to fix it WITHOUT A NOISE FILTER.

Items needed:

3-4 inches of 18-22 gauge wire.
Two MALE quick slide 22-18 gauge electrical connectors.

Now, to do this, you'll need a pair of wire strippers (or use your teeth, your choice) and wire crimpers.

1. Assemble everything you'll need. Ensure you know where the noise filter harness is in the car.
2. Take your wire and strip off about 1/2" on both sides.
3. Take the two connections and REMOVE THE OUTER CASE. I took a pair of pliers and yanked on the male side and locked the plastic part into a vice. A pair of pliers should also work. Take care to not crimp down on the wire crimp part yet.
4. Attach the two naked connections to the wire.
5. Bend the wire as shown in the picture below.
6. Slide wire into the noise filter harness plug.
7. Make sure it's tight, if not then secure it to the plug somehow.
8. Start the car and make sure the tach works.

It took me about 10 minutes to do this, but I have a good mechanical knowledge and background. Even a complete idiot should have this done in no more than an hour.

Notes:
1. The stock noise filters resistance measure 2.3 kilo ohms.
2. The wire resistance measured .2 kilo ohms.
3. I did not need to ground the wire for this to work.
4. I did not go on an extensive test drive to test this out, but the tach DID function throughout the entire RPM range.

If any questions, give me a buzz on here. Good luck DSMers!

MODS: can you please reflect the title to show resolved or say "Fix included" Thanks! It wouldn't let me do it myself.

Pictures.

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Items needed. I used house wire as it's very sturdy and fit just right. You'll see the parts to the left and assembled to the right.

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My noise filter and area of the plug. Right behind the intake manifold. If your noise filter is still attached then it's only a 10mm bolt holding it on.

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Fix bent to fit into the connection nice and snug.

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Fix installed and working.

Now if you are wanting to be SUPER right about this, then install a 2.3 kilo ohm resistor on the line and see if that works. I didn't need to.

-Brando

 

[19Eclipse90]

Well I got the filter installed. Guess what?

The bastard works. After all that heartache I could have just grabbed that little guy and been done with it.

Who would'a thunk?!

Glad you got it going. I know how nice it is to have all the gauges working.

Let us know if you try jumping wires and what happens. I don't think it will work, simply based on steve's statement I quoted above: the filtered signal is sent to the tachometer. But I know nothing of the signal's specifics like what the signal actually outputs and what the tachometer wants to read or can work with.

 

[1990AWD]

The noise filter is needed for the tach to work. It plugs into the harness below the intake manifold, right beside the knock sensor plug and it has to be grounded to something.

First post.

 

[obsidian]

My noise filter isn't grounded at all. It works great.

I'm doing research on what a noise filter actually is and basically trying to figure out how to make a new one with parts from radio shack.

 

[steve]

I don't have my 90 FSM here with me in London but it shows what the functional diagram is (something like a Resistor/Capacitor filter) If you knew the correct values you could replicate it. IF I remember correctly the factory one does two things, it splits the signal to go to two places, and filters the signal. One path goes to the tach and the other to the ECU.

If you own a 90 car you really should search eBay for the 90 FSM.

 

[obsidian]

I already have the FSM and I've researched it thoroughly and it hasn't shown me much as far as detailed explanations of certain parts.

I'm currently in contact with a company that does nothing but noise filters and I'm trying to see if there isn't a way I can test the working one I have now to find out what size/resistance it is so that I can post it up here for others to fix their own busted noise filters.

 

[EZSpeed]

Any luck with the filter? I just got a 90 and the tach doesn't work, but the speedo gauges go by 10s and as far as I know it's an awd...maybe the previous owner switched to a different cluster?
Anyways thanks for trying to get to the bottom of this problem. Where exactly is this filter located?

 

[obsidian]

The pictures earlier in the thread have the little guy on it. If I get a chance today I'll try to just jump the leads and see what happens. i'll let you know.

UPDATE WITH FIX. Get to it DSMers!

-----------------------------------------------------

Because of the auto merge feature....

Here is my theory on the noise filter and what it does/how it works. It's just a theory but it makes perfect sense to me. Anybody with extensive knowledge on this can rebuttel me at anytime.

A noise filter in electronics is essentially a resistor of a certain strength. Noise in electronics is often called "white noise" and it's little pulses from another system of normally very small strength. In a line with no resistors, the resistance is very low so the noise travels down and can interfere with other components.

My theory is that a noise filter of this strength, 2.3 kilo ohms, blocks ALL SIGNALS that is less than that. Basically it's like the sign at the carnival, you must be this strong to pass. That blocks white noise and only lets the true super strong signal through to the tach.

So what happens to the tach without a noise filter? I can only assume at this time that you may get little blips in the needle if you have a lot of white noise through the car's electronics system. Otherwise, if like on my car, the needle operated just fine without the resistor and allowed the signal to pass through.

I believe that on cars who's tachometer no longer works, the resistor finally gave out and separated from the wire, therefore blocking all signal and not letting the tach work. On vehicles that are intermittant, the heat/cold can change the metal just enough to let it make contact or separate it far enough to not let any signal through.

-Brando

 

[19Eclipse90]

Like I said, I'm no electrical genius. Within the limits of my electrical knowledge, all of that makes some sort of sense.

Thanks for spending the time to figure this out. We all know how difficult these are to find in a junkyard and a brand new noise filter is something like $45 from the dealer (if it's even available anymore). I imagine this ought to help a number of folks out.

Consider submitting the "fix" as a tech article and linking to this thread within it for discussion purposes.

 

[obsidian]

I will try to submit this fix for a tech. Thanks for the thought.

I'm frankly surprised that after 22 years, no one has done this. Just goes to show what some people are doing and not doing.

If anyone has any questions then please post up. Also, if this has fixed anyone's tachometer then please post up.

------------------------------

Fix is posted in tech!

 

[steve]

A resistor by itself isn't a filter. It simply reduces all the signals by some amount. A filter is selective, reducing some signals while passing others. The noise filter in a 90 is a simple first order low pass RC filter. Low-pass filter - Wikipedia, the free encyclopedia causing some frequencies to have a low impedance to ground while the rest pass through. As I said before the FSM doesn't show the values for either the resistor or capacitor.

 

[obsidian]

A resistor by itself isn't a filter. It simply reduces all the signals by some amount. A filter is selective, reducing some signals while passing others. The noise filter in a 90 is a simple first order low pass RC filter. Low-pass filter - Wikipedia, the free encyclopedia causing some frequencies to have a low impedance to ground while the rest pass through. As I said before the FSM doesn't show the values for either the resistor or capacitor.

And here I am getting showed up. . Thanks buddy. Sounds complicated.

 

[19Eclipse90]

In this case, Steve, is there any harm reducing the whole signal to a certain level? Obviously Mitsu engineered it as such, so it's more of a question as what harm it might have. I haven't the foggiest what the ECU does with the unfiltered signal.

 

[obsidian]

In my knowledge of basic electricity, the connection is not split into two at THAT connection. It's two wires, one is a supply for the signal, the other is to receive the filtered signal. So THAT connection i believe is solely for the tach.

Wouldn't the ECU take the RPM from the CAS?

 

[steve]

The ECU signal from the tach gate is labeled Ignition Pulse Detect. It's used by the ECU to sense that the coils fired. The ECU DOES use the CAS signal for RPM.

It possible that the noise filter is just that, a way to reduce the electrical noise produced from this signal so that it doesn't effect the radio rather than some sort of conditioning required for the gauge cluster. That would explain why just shorting the two pins makes the tach work as does a resistor between the two.

 

[EZSpeed]

I tried wiring it your way but haven't been able to start the car to see if it worked yet because I've got a leaky gas tank :-( but just so I'm on the same page you took out the noise filter altogether? and just connected the 2 hookups at the plug?

 

[obsidian]

I tried wiring it your way but haven't been able to start the car to see if it worked yet because I've got a leaky gas tank :-( but just so I'm on the same page you took out the noise filter altogether? and just connected the 2 hookups at the plug?

That's right.

 

[i3oi3c78]

This works great, my tach didn't work when I got the car. I've been trying to figure out this fix for awhile, only to come to dead ends. Thank you very much.

 

[obsidian]

Glad to be of service.

 

[Talondvr]

I'm hoping someone smarter than me can use these to possibly make a write up as to how to make these tachs interchange properly. Most people seem to have a problem with the tach filter. I only had a 90 tach with a 91 dsm, so i was hoping to add/make something to add to it to make it work.
Can someone with a 90 car modify a 91 transistor and tach or make a noise filter? Can someone with a 91 car modify a 90 transistor and tach?? Are the 2 signal completely different or can it be modified to work with each other??
Here are pics of the 90 and 91 tach with descriptions of the components. If no one here can figure it out it prya isn't worth it to try! I have all the components for a 90 and 91 ignition systems so If more info is needed I can prya get it.
https://docs.google.com/viewer?a=v&...MmJiYi00YmU2LWJlNTQtNDU0ODY5MGNlYjRj&hl=en_US
https://docs.google.com/leaf?id=0B9...NmM4OC00MWRhLTgyMWMtODUxZmNkODJkNGFj&hl=en_US
https://docs.google.com/leaf?id=0B9...ZGEzNy00MzlmLTk2OWYtMjkzMjgzYmY5MmFk&hl=en_US
https://docs.google.com/leaf?id=0B9...MzFhNi00NTk1LWI0NzgtMmYxMWIxNGRjY2Vl&hl=en_US
https://docs.google.com/leaf?id=0B9...M2JkMC00YzVlLTgxMTgtMjkwNzlmY2Q3MTI0&hl=en_US
https://docs.google.com/leaf?id=0B9...M2U1Zi00OWMxLWFmMmYtZjc2ZmQ3M2RhNTdj&hl=en_US

 

[obsidian]

Talondvr, if you have a 91 model with a 90 tach, I'm not sure of anyway to make it work other than you need to get a 91-94 tach. The 90 system is way too screwy to modify your good and much better 91 harness.

In all honesty, using a 91 tach is much much much better than swapping over your better wiring for the craziness that is the 90 wiring.

 

[Talondvr]

Ya, I gave up hope and found a 91 tach for it, but I figured if its doable someone here can figure it out. Someone one day may be able to use the info so I posted it.

 

[EZSpeed]

late reply, but i finallly got my car up and running and this fix works! awesome find

 

[obsidian]

Good deal. I actually got my hands on a spare noise filter so if anyone is looking then PM me.

 

[obsidian]

Spare noise filter has been sold.

 

[1990laserrsred]

my 90 Laser tach did not work for years, i tried a new gauge cluster, cleaning all leads and grounds, replaced two noise filters, and two tacho interfaces. End the end the bypass of the noise filter worked!!!!!!! after 11 or 12 years my tach finally works, this bypass is awesome. looks like the it was the damn noise filter.